Added a small mental arithmatic game

site/mental-arithmatic/style.css

@@ -0,0 +1,99 @@
+.hidden {
+    display: none !important;
+}
+
+body {
+    min-height: 100dvh;
+    --pico-form-element-disabled-opacity: 1.0;
+}
+
+.game-card {
+    display: flex;
+    flex-direction: column;
+    min-height: 80dvh;
+}
+
+.game-card header,
+.game-card footer {
+    display: flex;
+    justify-content: space-between;
+
+    font-size: 2em;
+    margin-block: 12px;
+    margin-inline: 20px;
+}
+
+.game-card main {
+    flex-grow: 1;
+    flex-shrink: 1;
+
+    display: flex;
+    align-items: center;
+}
+
+.game-card .question {
+    margin: auto;
+    width: 60vw;
+
+    text-align: right;
+    font-size: 3em;
+}
+
+.game-card .answer {
+    border-block: 2px solid black;
+    padding-block: 2px;
+    position: relative;
+}
+
+.game-card .answer.right {
+    border-color: green;
+    color: green;
+}
+
+.game-card .answer.wrong {
+    border-color: red;
+    color: red;
+}
+
+.game-card .answer .indicator {
+    display: none;
+    position: absolute;
+    top: 0;
+    bottom: 0;
+    left: 0;
+}
+
+.game-card .answer.right .indicator.right {
+    display: block;
+}
+
+.game-card .answer.wrong .indicator.wrong {
+    display: block;
+}
+
+.game-card .question input {
+    border-inline: none;
+    border-radius: 0;
+    box-shadow: none;
+
+    border: none;
+
+    margin: 0;
+    padding: 0;
+
+    text-align: right;
+    font-size: 1em;
+    height: 1em;
+}
+
+.game-card .question input:focus {
+    border-none: none;
+}
+
+.game-card .answer.right input {
+    color: green;
+}
+
+.game-card .answer.wrong input {
+    color: red;
+}