.grid_container {
  display: grid;
}
.grid_content {
    grid-area: 1 / 1 / 2 / 2;
}

/* Loading container */
#loading_content {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    opacity: 1;
    transition: opacity 0.3s ease-in-out; /* Smooth transition effect */
}
#loading_content.is-hidden {
    opacity: 0;
}
#loading_content.is-visible {
    opacity: 1;
}

/* Loading icon */
#loading_icon {
    position: fixed;
    border: 16px solid #f3f3f3;
    border-radius: 50%;
    border-top: 16px solid blue;
    border-right: 16px solid green;
    border-bottom: 16px solid red;
    border-left: 16px solid pink;
    width: 120px;
    height: 120px;
    -webkit-animation: spin 2s linear infinite;
    animation: spin 2s linear infinite;
}

/* Loading icon */
#loading_svg_icon {
    position: fixed;
    width: 120px;
    height: 120px;
    filter: invert(0.5) sepia(1) saturate(5) hue-rotate(175deg);
}

@-webkit-keyframes spin {
    0% { -webkit-transform: rotate(0deg); }
    100% { -webkit-transform: rotate(360deg); }
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* Initial hidden state */
#body_content {
    opacity: 0;
    transition: opacity 0.3s ease-in-out;
}
#body_content.is-visible {
    opacity: 1;
}

/* Initial hidden state */
.logo {
    opacity: 0;
    transition: opacity 1s ease-in-out;
}
.logo.is-visible {
    opacity: 1;
}

/* Initial hidden state */
.add_item {
    opacity: 0;
    transition: opacity 1s ease-in-out;
}
.add_item.is-visible {
    opacity: 1;
}

.item_00 {
    opacity: 0;
}
.item_00.is-visible {
    opacity: 1;
}
.button_container.item_00 {
    transition: color 0s ease, background-color 0s ease, font-size 0s ease ;
}

.item_01 {
    opacity: 0;
}
.item_01.is-visible {
    opacity: 1;
}
.button_container.item_01 {
    transition: color 0.5s ease, background-color 0.5s ease, font-size 0.5s ease, opacity 0.5s ease ;
}

.item_02 {
    opacity: 0;
}
.item_02.is-visible {
    opacity: 1;
}
.button_container.item_02 {
    transition: color 1.0s ease, background-color 1.0s ease, font-size 1.0s ease, opacity 1.0s ease ;
}

.item_03 {
    opacity: 0;
}
.item_03.is-visible {
    opacity: 1;
}
.button_container.item_03 {
    transition: color 1.5s ease, background-color 1.5s ease, font-size 1.5s ease, opacity 1.5s ease ;
}

.item_04 {
    opacity: 0;
}
.item_04.is-visible {
    opacity: 1;
}
.button_container.item_04 {
    transition: color 2.0s ease, background-color 2.0s ease, font-size 2.0s ease, opacity 2.0s ease ;
}

.item_05 {
    opacity: 0;
}
.item_05.is-visible {
    opacity: 1;
}
.button_container.item_05 {
    transition: color 2.5s ease, background-color 2.5s ease, font-size 2.5s ease, opacity 2.5s ease ;
}

.item_06 {
    opacity: 0;
}
.item_06.is-visible {
    opacity: 1;
}
.button_container.item_06 {
    transition: color 3.0s ease, background-color 3.0s ease, font-size 3.0s ease, opacity 3.0s ease ;
}